Microporous polymeric poly(aryl ether) membranes that include polysulfone and polyphenylene oxide membranes are well known in the art and are used widely for filtration and purification processes, such as filtration of waste water, preparation of ultrapure water and in medical, pharmaceutical or food applications, including removal of microorganisms, dialyses and protein filtration. The polysulfone membranes are manufactured from a number of polysulfone type polymers, including bisphenol A based polysulfone, biphenyl based polysulfone and polyether sulfone. While these membranes have found broad utility for a variety of purposes, they suffer from several disadvantages, such as a broad and frequently non uniform pore size distribution, and susceptibility to fouling. The microporous membrane materials are frequently divided into two categories based on pore size: microporous and mesoporous. Microporous materials typically contain pores with diameter greater than 50 nm, while mesoporous materials are usually defined as those with pore diameter in the range of 2–50 nm. It is particularly difficult to prepare mesoporous poly(aryl ether) membranes.
Preparation of porous poly(aryl ether) membranes is well known in the art. Phase inversion method has been used extensively for the preparation of such membranes. The membranes thus obtained are frequently asymmetric with graded pore size across the cross section. Such membranes are frequently mechanically weak and the amount of open pore space on the surface of the membrane as a fraction of the available surface area is relatively small, as disclosed for example, by Kools, W., in WO Patent 0189672 A1; 2001.
U.S. Pat. Nos. 3,852,388 and 4,944,775 disclose preparation of asymmetric poly(phenylene oxide) membranes. The process involves forming a solution of the poly(phenylene oxide) in a solvent system, forming a nascent membrane from the solution, followed by coagulating the nascent membrane in a coagulation bath formed from a liquid that is miscible with the solvent system but is a non-solvent for the poly(phenylene oxide) polymer. Preparation of porous poly(phenylene oxide) hollow fiber membranes is described by S. Berghams et al. in the article entitled “Spinning of hollow porous fiber via the TIPS mechanism”, Journal of Membrane Sciene, Volume 116, page 171–184, 1996, and by J. Smid et al. in the article entitled “The formation of asymmetric hollow fiber membranes for gas separation, using PPE of different intrinsic viscosities”, Journal of Membrane Science, Volume 64, page 121–128, 1991. The porous hollow fibers are produced by a solution based spinning process wherein the nascent hollow fibers are solidified by a thermally induced quenching or by a coagulation in a non-solvent.
Preparation of highly asymmetric, anisotropic polysulfone membranes is disclosed in U.S. Pat. Nos. 5,886,059 and 5,958,989. Also known is the preparation of polysulfone membranes with a mixed isotropic and anisotropic structure as disclosed, for example, in U.S. Pat. No. 5,906,742, and preparation of isotropic polysulfone membranes as described by A. L. Ly et al. in U.S. Pat. No. 4,970,034.
It is also known to produce porous poly(aryl ether) membranes, including porous polysulfone membranes by a melt extrusion process. For example, T. B. Meluch et al. in U.S. Pat. No. 6,218,441 disclose preparation of polysulfone semipermeable membranes from polysulfone mixture with a solvent, and a non-solvent by a melt extrusion process.
It is also known to produce multilayer porous membranes or porous membranes comprised of multiple porous zones. Preparation of reinforced, three zone microporous membranes is, for example, disclosed by M. T. Meyering et al. in U.S. Pat. No. 6,513,666. Such multizone porous membranes are known to provide improved mechanical properties, particularly in fluid separation applications that require periodic backwashing, are known to exhibit a lower cross membrane pressure drop, a decreased susceptibility to breach of the membrane separation layer and a decreased propensity of fouling.
A recent report by Y. Ding and B. Bikson entitled “Novel macro and meso porous materials prepared from polysulfone/polyimide blends” in “Material Research Society Symposium Proceeding”, Volume 752, AA1.3, Boston, 2002, describes preparation of porous polysulfone films from its blends with a phenylindane containing polyimide by decomposing the phenylindane containing polyimide with a hydrazine solution in methanol. However, the use of hydrazine based chemical system is hazardous and complex. Thus, there still remains a need in the art to produce poly(aryl ether) porous articles, including porous membranes, with improved properties by a simple and commercially benign method that does not utilize hazardous chemicals in membrane fabrication.